/Engine/Plugins/FX/Niagara/Source/NiagaraEditor/Public/NiagaraGraph.h
Returns the index of this variable in the output node of the graph. INDEX_NONE if this is not a valid attribute.
int32 GetOutputNodeVariableIndex ( const [FNiagaraVariable](API\Plugins\Niagara\FNiagaraVariable) & Attr ) const